Energy converter to power circulatory support systems

ABSTRACT

An energy converter of the Stirling cycle engine type to function as a power source for an artificial heart. The engine is designed to produce 1 to 10W to a blood pump operating at 60 to 150 pulses per minute. The simplified Stirling type engine includes a moving regenerator which is operated by pneumatic power produced within the engine itself made possible by the drive chamber, drive piston, and novel arrangement of springs and valves which maintain the engine chamber at a constant volume during compression and decompression, thereby, increasing engine output.

United StatesPatent [1 Noble et al.

[ Jan. 29, 1974 ENERGY CONVERTER TO POWER CIRCULATORY SUPPORT SYSTEMS [75] Inventors: Jack E. Noble, Benton City; Richard P. Johnston, Kennewick, both of Wash.

[73] Assignee: The United States of America as represented by the Secretary, Department of Health, Education and Welfare, Washington, DC.

22 Filed: Mar. 4, 1971 21 Appl. No.: 121,069

[52] US. Cl 417/207, 60/24, 62/6, 92/605, 417/392 [51] Int. Cl. F04b 19/24 [58] Field of Search 417/392, 394, 395, 207; 60/24; 62/6; 92/605 [56] References Cited UNITED STATES PATENTS 3,478,695 1 1/1969 Goranson et al. 60/24 X REGENERATOR FROM LOAD 3,513,659 5/1970 Martini 62/6 3,604,821 9/1971 Martini 60/24 X 3,563,028 2/1971 Goranson et al. 60/24 1,586,278 5/1926 Bardenheuer 92/605 Primary Examiner-Carlton R. Croyle Assistant Examiner-Richard Sher Attorney, Agent, or Firni-Browdy & Neimark [57] ABSTRACT 9 Claims, 5 Drawing Figures PAIENIEBJANZSIHH 3.788.772

' SHEET 1 [1F 2 HEAT SOURCE-* REGENERATOR1' i B D ENGINE L I, CYLINDE'R i C L B IDEAL SCl-gsLDT WORKING GA$-- um L I VENTIONAL ENGINE) POwER PIsTON A HEAT SINK mm m IDEAL CYCLE w (SIMPLIFIED a: sTIRLING l3 8 ENGINE) FLYWHEEL w 2 3 MECHANICAL g LINKAGE O.

. (I) COMPRESSION HEATING EXPANSION COOLING g CONVENTIONAL ENGINE ,4 I 4 HEAT souRCE-- GAS VOLUME REGENERATOR A /0 4 ENGINE CYLINDER 1 3 I I /5 WORKING GAs I HEAT SINK OuTLET PUMP DIAPHRAG VALVE INLET vALvE I I I J PUMP sTART PUMP I sTART FULL PUMPING EMPTY FILLING SIMPLIFIED ENGINE FIG,

, 2/ COOLING MODULEI jr ELECTRIC ELECTRIC POWER HEATER //8' ENGINE BLOOD AND MOTOR THERMAL GAs PUMP l6 STORAGE CoMPREssoR I A I CONTROL I MODULE J ENGINE MoDuLE PUMP MODuLE INVENTORS FIG. 2

ATTORNEYS ENERGY CONVERTER TO POWER CIRCULATORY SUPPORT SYSTEMS FIELD OF THE INVENTION The invention relates to energy converters and, more particularly, to energy converters of the Stirling cycle, free piston, heat utilization type which produce a desired pressure at a desired pulse frequency and which include a thermal storage reservoir for use when the source of input heat is lacking.

BACKGROUND OF THE INVENTION There occurs sometimes a situation wherein it is necessary to surgically bypass the living heart of an individual while at the same time making absolutely sure that the body of the individual has the necessary blood flow to oxygenate and feed its cells. In open-heart surgery, for example, where a rupture in one of the valve chambers of the. heart has occurred, or where one of the hearts valves needs repair, the surgeon must rely on an artificial heart machine to keep the patient alive while he is performing the delicate surgery. The artificial heart machine functions to pump blood to the lungs where it is aerated before being circulated throughout the body, in much the same manner that a live heart operates.

While this sequence of events is occurring it is imperative, at the cost of life or death, that the artificial heart operate without fail, and as nearly as possible to the pressure and repetition rate of a living heart. Failure of the motive power to the artificial heart machine would mean instant death to the patient, so its importance cannot be over-stressed.

While prior art sources-of power have been somewhat satisfactory, they nevertheless are lacking in some aspects and do possess certain shortcomings. Even with electric power there is frequently a power failure, and other energy converters can be inefficient and costly to operate.

SUMMARY OF THE INVENTION The present invention offers improvements over the prior art in that it involves a mechanism to drive the freely oscillating regeneratoror displacer of a free piston type Stirling or heat engine. The system utilizes the varying pressure within the engine cylinder to provide a net driving force on a piston which is attached to the regenerator or displacer, and the system possesses the following features which are inherent in the system and which are improvements over other systems:

1. Stable and reliable operation over a wide range of operating conditions is economically assured because substantial reserve power can be designed into the system and yet be conserved when not required. Prior systems, on the other hand, wastefully dissipate reserve power when not used.

2. The tendency of the regenerator or displacer to oscillate asymmetrically about the centerpoint of the en gine due to preferential leakage of working gas around the piston seal is reduced or eliminated by the pressure equalization that occurs due to venting between the engine and drive chambers at each end of the stroke.

3. The power output of the engine can be simply and conservatively controlled.

Many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of an exemplary embodiment when considcred in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF PREFERRED EMBODIMENT Referring to FIG. 1 for a brief comparison of a conventional Stirling engine and simplified type similar to that used in the present invention, there is shown schematically the four phases of the cycle, the regenerator drive mechanism having been omitted for clarity in each case. Also in the conventional engine a crank and flywheel cause regenerator motion to lead power piston motion by 90. Therefore, in FIG. 1 there is shown an engine 10 having an engine chamber 11, inside of which there is movably positioned a power piston 12,

I the piston 12 being mechanically connected by suitable chamber 11 so as to cooperate with piston 12.

In the conventional Stirling engine, compression takes place with the gas generally in the cold portion of the engine (lower pressure) and expansion takes place with the gas generally in the hot portion of the engine (higher pressure) In this cycle, the four phases of the heat engine overlap and give a rounded indicator diagram, as shown in the corner of FIG. 1.

In a simplified Stirling engine, such as one disclosed in the present invention, the regenerator is moved independently by any number of means, and generally the power piston is unnecessary and therefore omitted entirely. In the lower portion of FIG. 1, the engine is shown as a liquid pump, and from position 1 to 2, the system is pressurized to the outlet pressure for the liquid pump. From 2 to 3, the outlet valve is open and liquid is forced out. From 3 to 4, both valves are closed and the pressure drops to the inlet pressure. From 4 to l, the inlet valve is open and new liquid is drawn in. The cycle then repeats.

In FIG. 2 there is shown a typical energy system concept for use as an artificial heart power source, using a simplified Stirling engine, such as disclosed by this invention. The block diagram shows a source of electric power 16 which is used to heat an electric heater to drive a simplified Stirling engine 10. Engine 10, in the preferred embodiment, is used to produce a supply of compressed air, in pulses of the required pressure and frequency, resembling those of a normal living heart, this compressed air being applied as motive power to a pneumatic motor 17. Motor 17, in turn, drives a blood pump 18 having suitable valves and input and output connections to the blood system of a patient undergoing treatment or surgery. A control module 20 receives operating Signals from pump 18 and applied like signals to engine and pneumatic motor 17 to maintain accurate blood flow. A cooling module 21, in the form of a water jacket of fluid filled tubes, surrounds one end of the engine to provide a greater temperature differential between the hot and the cold working gases.

Turning now to FIG. 3 there is shown a schematic view of the simplified Stirlingengine comprising the subject matter of the instant invention. The engine 10 has a chamber 1 l, a heat source 14 from a hot face, and a regenerator l5. Forming a part of regenerator l5 and integrally attached to the lower face thereof, is a drive piston 22, which works back and forth into a drive chamber 23. Drive chamber 23 forms a part of, and is an extension of engine chamber 11, but is somewhat smaller in bore. The lowermost end of drive piston 22 has a plate 24 attached transversely to the piston, with short projections 25 extending beyond the sides of the piston.

Attached to plate 24, and therefore to piston 22, there is a primary spring .26, the spring 26 being connected between the piston and some fixed anchoring means as at 27. Fastened'to the end wall of drive chamber 23 are a pair of rebound springs 28, these springs being fastened at one of their ends and having the other end free and extending along the longitudinal axis of the drive chamber so that they will contact projections 25 when drive piston 22 is in its lowest position. By means of this arrangement when the drive piston has reached the lower limit of its travel, springs 28 will not only act as a cushion against further travel in that direction, but will urge the piston to reverse its direction toward upward movement.

The opposite wall of engine chamber 11 from the hot faces 14 comprises a cold face 30, which as the name implies is relatively cool, and the gas in contact with this area is understandably at relatively low pressure. An aperture in the center of cold face 30 provides for the passage of drive piston 22, while attached to the underside of the face there is a second set of rebound springs 31 which cooperate with projections 25 on the upward stroke of piston 22, to again reverse direction of the piston.

In order to provide for the delivery of gas to the engine, and laterfor its delivery to a load (here the pneumatic motor which drives the blood pump), there is furnished a low pressure input channel 32 and a high pressure output channel 33. A main intake valve 34 admits the low pressure gas from input channel 32 into engine chamber 11 while an auxiliary intake valve 35 admits a lesser amount of gas into drive chamber 23. On the other side of the engine a main exhaust valve 36 conducts high pressure gas to the output channel 33 while an auxiliary exhaust valve 37 conducts a lesser amount of gas also to output channel 33. It should be understood that valves 34, 35, 36 and 37 are check valves which are spring biased in a closed position.

It was discovered that an easy and effective way of controlling the power output of the engine is by varying its stroke and frequency. This can be readily accomplished by means of a variable volume chamber 38 which adjoins the end of drive chamber 23 and is made of bellows-like pleats of some flexible material. Thus by compressing or extending the variable volume chamber 38 by adjustable means, not shown, the effective volume of the drive chamber 23 is likewise varied, resulting in a variation of power output from the engine.

In FIG. 4 there is shown a displacement chart wherein pressure is plotted against displacement, and an interpretation of the chart will be given hereinafter.

So as to maintain operation of the engine should electricity be cut off from the heater surface 14, the modification of FIG. 5 shows the use of a thermal storage reservoir 40 associated with the regenerator 15. Analysis showed that too much thermal resistance would be encountered if this reservoir were placed between the heater 14 and regenerator 15. Therefore, as shown in FIG. 5 the arrangement was reversed and a new type heater was placed between the reservoir and the regenerator. To further improve thermal insulation of the engine, and also to obtain a higher temperature differential of the working gas (argon was found to be best) the entire engine was encased in a water cooled Bell Jar 41, cooling being obtained from coils 42, and the engine being insulated from the Bell Jar by insulation 43 (preferably vacuum).

The thermal storage device 40 receives heat from the electrical heater 14 during the charge cycle and stores the heat for maintenance of engine operation during the period of electricity cut-off. Heat storage is accomplished by using a salt, such as lithium hydride, for example, which melts at engine operating temperatures. Thermal energy is stored as latent heat of fusion and released during recrystallization. The engine module will operate for 25 minutes at peak power output (13w) and 50 minutes at the average power output (4w) with the electric heater turned off.

Operation of a conventional Stirling engine and that of a typical simplified engine having been given supra, turn now to the operation of the engine comprising the present invention, as shown in FIG. 3 and related to the chart of FIG. 4.

FIG. 4 is a pressure displacement diagram for the engine and drive chambers 11 and 23 respectively. Point A (FIG. 4) corresponds to a position of the regenerator 15 adjacent to the hot face, or heater 14. Energy stored in the primary spring 26, and in the rebound springs 31 causes the regenerator 15 to move downwardly toward the cold face 30. The gas is heated as it passes through the porous regenerator 15 causing the engine chamber pressure to rise. As the drive piston 22 enters the drive chamber 23 the pressure in that chamber also increases due to the volume reduction, but at a lesser rate than in the engine chamber. The resulting pressure differential (AP) acts on the drive piston 22 in a direction which sustains the motion. The driving force is equal to the pressure differential times the drive piston cross section area.

When the engine pressure reaches exhaust pressure (Point B) gas begins to discharge from engine chamber 11 through the main exhaust valve 36 into the high pressure output channel 33 to the load, which is in this case the pneumatic motor 17. A short time later the drive chamber pressure reaches exhaust pressure (Point B) and gas from the drive chamber 23 is discharged through the auxiliary exhaust valve 37 into the output chamber 33 to pneumatic motor '17. Throughout the balance of the stroke, motion is sustained by energy stored in the primary spring 26 and the inertial energy of the moving mass. At the end of the stroke (Point C) the regenerator 15 comes to rest. The energy of motion (with the exception of that dissipated by damping forces) is now stored in primary spring 26 and rebound springs 28, the latter having been compressed by projections 25 on plate 24 when the drive piston came to rest. Springs 26 and 28 then reverse the motion and the process proceeds in the reverse direction.

Upon return, the energy built up in primary spring 26 and in rebound springs 28 causes the regenerator to move upwardly toward the hot face 30. The gas is cooled as it passes through the porous regenerator 15 causing the engine chamber pressure to decrease. As the drive piston 22 leaves the drive chamber 23 the pressure in that chamber also decreases due to the increase in volume, but at a lesser rate than in the engine chamber. Again, the resulting pressure differential acts on the drive piston 22 in a direction which sustains the motion.

When the engine pressure reaches intake pressure (Point D) gas begins to enter engine chamber 11 through main intake valve 34 from input channel 32. A short time later the drive chamber pressure reaches intake pressure (Point D) and gas from the input channel 32 enters drive chamber 23 through the auxiliary intake valve 35. Throughout the balance of the stroke, motion is sustained by energy in the primary spring 26 and the inertial energy of the moving mass. At the end of the stroke (Point A) the regenerator 15 comes to rest. The energy of motion (with the exception of that dissipated by damping forces) is now stored in primary spring 26 and rebound springs 31, the latter having been compressed by projections 25 on plate 24 when the drive piston came to rest. Springs 26 and 31 then reverse the motion and the process starts all over again.-

At steady state operation, the energy imparted to the moving mass system is equal to the energy dissipated by windage, friction, and other losses. The energy used to drive the regenerator 15 is represented by the shaded area of the diagram of FIG. 4, while the unshaded area represents energy delivered to the load from the drive chamber.

If, due to increased friction, the energy requirement to sustain the oscillation increases, the delivered energy can be increased by increasing the drive chamber volume. This is accomplished by adjusting the variable volume chamber 38. The pressure in the drive chamber 23 then rises less rapidly as is indicated by the dashed lines (FIG. 4). The energy which drives regenerator 15 is then represented by the areas ABB and CDD". Again, the balance of the area of the diagram, A, B" C D", represents energy delivered to the load. By sufficiently increasing the volume of the drive chamber, the energy represented by the total area of the diagram can be used to drive the regenerator if it is required. The system thus provides a large reserve power to drive the regenerator, yet conserves that power if it is not required. Control of engine power output is implicit in the foregoing and is discussed below.

As a means of engine control, the power'output of the engine can be varied by varying the stroke and frequency. A reduction in power output is thus accomplished by decreasing the volume of drive chamber 23 through variable volume means 38. The pressure in drive chamber 23 then rises more rapidly and less energy is imparted to the spring-mass system. With less driving energy, the amplitudeof the oscillation de creases. Rebound springs 28 and 31 are now engaged for a lesser portion of the stroke which reduces the effective spring constant of the combined primary (26) and rebound (28, 3]) spring system which results in a reduced frequency of oscillation. The stroke and frequency are thus simultaneously reduced. The output of the engine is naturally increased by the reverse proce' dure, the limit being obtained when full engine stroke is achieved.

As disclosed previously, in the modification of FIG. 5, a thermal storage reservoir 40, may be attached to and form an integral part of, regenerator 15, to serve as an emergency source of heat should electricity supplying heater 14 be cut off. When such a reservoir is being utilized its enclosed area is filled with a thermal energy storage material such as lithium hydride, for example, or a salt which melts at engine operating temperatures. In operation, then, thermal energy is stored as latent heat of fusion where the lithium melts and heat is released during recrystallization to maintain the engine module in operation in the order of 25 minutes at peak power (13w) and 50 minutes at average power output (4w).

As a brief summary, operation of the engine should be quickly reviewed, realizing that four processes are involved; intake, compression, exhaust and decompression:

1. intake When the regenerator is near the engine hot plate, the engine is filled with cold gas. Resulting low engine pressure opens the intake valve, permitting low pressure gas to enter the engine.

2. compression When the regenerator moves away from the hot plate, the displaced gas is heated, causing pressure to increase. A pressure difference occurs across the drive piston because engine pressure increases faster than drive piston chamber pressure. This pressure difference supplies sufficient energy to overcome regenerator windage and support system friction.

3. exhaust When the regenerator nears the cold plate, high pressure gas is discharged into the high pressure line.

4. decompression As the regenerator moves away from the cold plate, the displaced gas is cooled, causing engine pressure to decrease. Again, energy is supplied to the drive piston since engine pressure decreases faster than drive piston chamber pressure.

While the description of the invention has been directed to an energy conversion system to serve as a power source for an artificial heart, and as such by popular experience it is associated with an external heart machine for open chest surgery, it should at the same time be realized that the device can be completely implantable within the body of an animal for in vivo experiments. The entire engine module is of sufficient size and weight to perform such experiments since the module occupies 0.477 liter, weighs 619 g., and produces 13.3w at a frequency of 10 cps. The engine cylinder contains argon as the working gas, and space is provided for sufficient thermal storage material for animal in vivo test demonstration purposes.

From the above description of the structure and operation of the invention, it is obvious that the disclosed device offers a new and novel energy converting system which overcomes many weaknesses and undesirable features of prior systems. The invention thus disclosed a heat utilization, free piston engine of the Stirling cycle type which has been simplified and improved to furnish power at a specified pressure and pulse frequency so that it can be used to drive an artificial heart apparatus. Means are also included, in the form of a thermal storage reservoir, to keep the apparatus in operation should heater potential be discontinued, and particularly should be apparatus be implanted in an animal for in vivo experimentation.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A source of pulsatile fluid pressure, comprising:

an engine chamber filled with working fluid;

a movable porous regenerator mounted within said engine chamber; 1

means acting upon said regenerator for oscillating said regenerator in said engine chamber;

a drive chamber filled with said working fluid;

piston means connected to said drive chamber and said engine chamber for increasing and decreasing the fluid pressure within said drive chamber in response to the motion of said regenerator, wherein said piston means comprises a piston connected to said regenerator and extending from said engine chamber into said drive chamber; and

means for transmitting pressure pulses of said working fluid from said engine chamber and said drive chamber to a load and back to said engine chamber and said drive chamber] 2. The device of claim 1 wherein the drive chamber further includes adjustable means for regulating the power output of the source of pulsatile fluid pressure.

3. The device of claim 2 wherein said adjustable means comprises means for altering said drive chamber.

4. A source of pulsatile fluid pressure in accordance with claim 1 further including:

means connected to said drive chamber and said engine chamber for equalizing the fluid pressure within said chambers at the end of each regenerator oscillation.

5. In an energy conversion system for supplying pulsatile fluid pressure to drive a motor and pump in an artificial heart, the improvement wherein the source of the pulsatile fluid pressure is a simplified Stirling type engine comprising: 1 I

. an engine chamber filled with working fluid;

a movable porous regenerator mounted within said engine chamber;

means acting upon said regenerator for oscillating said regenerator in said engine chamber;

a drive chamber filled with said working fluid;

piston means connected to said drive chamber and said engine chamber for increasing and decreasing the fluid pressure within said drive chamber in response to the motion of said regenerator, wherein said piston means comprises a piston connected to said regenerator and extending from said engine chamber into said drive chamber; and I means for transmitting pressure pulses of said work ing fluid from said engine chamber and said drive chamber to a load and back to said engine chambe and said drive chamber.

6. An energy conversion system in accordance with claim 5 wherein said source of pulsatile fluid pressure further includes:

means connected to said drive chamber and said ongine chamber for equalizing the fluid pressure wherein said chambers at the end of each regenerator oscillation.

7. In an energy conversion system for supplying pulsatile fluid pressure to drive a motor and pump in an artificial heart, the improvement wherein the source of the pulsatile fluid pressure is a simplified Stirling type engine comprising:

an engine chamber including a relatively hot surface at one end and a relatively cold surface at the other end, a side wall connecting the two ends and filled with a working fluid, and further including main intake and exhaust valves;

a movable, porous regenerator means mounted within said engine chamber and adapted to be reciprocated towards and from said hot and cold surfaces in said chamber;

a movable drive piston attached at one end to said regenerator meansand extending through the cold wall of said engine chamber means;

means for defining a drive chamber, said drive chamber means housing the other end of said drive piston and being filled with said working fluid, said drive chamber means further including auxiliary intake and exhaust valves, primary springs which resiliently attach said drive piston thereto, and rebound springs;

a first passageway leading toward both said main and auxiliary intake valves and filled with said working fluid; and

a second passageway leading away from both said main and auxiliary exhaust valves and filled with said working fluid;

whereby the motion of said regenerator and said drive piston produces pulsatile fluid pressure within said passages.

8. The device of claim 7 wherein the drive chamber further includes adjustable means for regulating the power output of the source of pulsatile fluid pressure. 9. The device of claim 8 wherein said adjustable means comprises means for altering said drive chamber. 

1. A source of pulsatile fluid pressure, comprising: an engine chamber filled with working fluid; a movable porous regenerator mounted within said engine chamber; means acting upon said regenerator for oscillating said regenerator in said engine chamber; a drive chamber filled with said working fluid; piston means connected to said drive chamber and said engine chamber for increasing and decreasing the fluid pressure within said drive chamber in response to the motion of said regenerator, wherein said piston means comprises a piston connected to said regenerator and extending from said engine chamber into said drive chamber; and means for transmitting pressure pulses of said working fluid from said engine chamber and said drive chamber to a load and back to said engine chamber and said drive chamber.
 2. The device of claim 1 wherein the drive chamber further includes adjustable means for regulating the power output of the source of pulsatile fluid pressure.
 3. The device of claim 2 wherein said adjustable means comprises means for altering said drive chamber.
 4. A source of pulsatile fluid pressure in accordance with claim 1 further including: means connected to said drive chamber and said engine chamber for equalizing the fluid pressure within said chambers at the end of each regenerator oscillation.
 5. In an energy conversion system for supplying pulsatile fluid pressure to drive a motor and pump in an artificial heart, the improvement wherein the source of the pulsatile fluid pressure is a simplified Stirling type engine comprising: an engine chamber filled with working fluid; a movable porous regenerAtor mounted within said engine chamber; means acting upon said regenerator for oscillating said regenerator in said engine chamber; a drive chamber filled with said working fluid; piston means connected to said drive chamber and said engine chamber for increasing and decreasing the fluid pressure within said drive chamber in response to the motion of said regenerator, wherein said piston means comprises a piston connected to said regenerator and extending from said engine chamber into said drive chamber; and means for transmitting pressure pulses of said working fluid from said engine chamber and said drive chamber to a load and back to said engine chambe and said drive chamber.
 6. An energy conversion system in accordance with claim 5 wherein said source of pulsatile fluid pressure further includes: means connected to said drive chamber and said engine chamber for equalizing the fluid pressure wherein said chambers at the end of each regenerator oscillation.
 7. In an energy conversion system for supplying pulsatile fluid pressure to drive a motor and pump in an artificial heart, the improvement wherein the source of the pulsatile fluid pressure is a simplified Stirling type engine comprising: an engine chamber including a relatively hot surface at one end and a relatively cold surface at the other end, a side wall connecting the two ends and filled with a working fluid, and further including main intake and exhaust valves; a movable, porous regenerator means mounted within said engine chamber and adapted to be reciprocated towards and from said hot and cold surfaces in said chamber; a movable drive piston attached at one end to said regenerator means and extending through the cold wall of said engine chamber means; means for defining a drive chamber, said drive chamber means housing the other end of said drive piston and being filled with said working fluid, said drive chamber means further including auxiliary intake and exhaust valves, primary springs which resiliently attach said drive piston thereto, and rebound springs; a first passageway leading toward both said main and auxiliary intake valves and filled with said working fluid; and a second passageway leading away from both said main and auxiliary exhaust valves and filled with said working fluid; whereby the motion of said regenerator and said drive piston produces pulsatile fluid pressure within said passages.
 8. The device of claim 7 wherein the drive chamber further includes adjustable means for regulating the power output of the source of pulsatile fluid pressure.
 9. The device of claim 8 wherein said adjustable means comprises means for altering said drive chamber. 